This apparatus is directed to an improved degasser. The degasser of this disclosure should be contrasted with the teaching of the art in degassers. As an example, the patent of Long U.S. Pat. No. 3,201,919 shows a degasser with a cylindrical housing and screw. By and large, a vortex is achieved in that device which moves the gas bubbles inwardly towards the axis of the rotating shaft. The Griffin U.S. Pat. No. 3,325,974 refers more aptly to spray tanks and the like. U.S. Pat. No. 3,856,483 shows a large bowl which rotates with a very thin film on it. The thin film is subjected to centrifugal forces. The heavier mud particles are centrifuged outwardly along the bowl and surrender their gas bubbles. Perhaps the vertically deployed screws in U.S. Pat. Nos. 3,229,449 and 4,199,322 disclose devices with a helical screw. In the '449 patent, a helical screw lifts the slurry of interests to enable it to cascade over a series of degassing plates 18, 19, 20 and 21. As it tumbles downwardly, degassing is encouraged. In the other, a helical screw leaves a central void to enable gas to rise in the central void.
The apparatus of this disclosure accomplishes degassing in an improved manner. Moreover, this apparatus has a central upstanding main housing which is axially hollow. Gas cut mud is introduced into it to be lifted by a helical screw. The helical screw extends above the topmost part of the cylindrical housing. It lifts the mud as far as the mud can travel, the mud spilling out through a laterally located opening. It extends taller, defining a gas flow path upwardly out through an exhaust fan. This feature coupled with variations in the spacing of the flights of the auger separates the mud from the gas which is entrained in the mud. This separation is enhanced by sloping the auger downwardly as it extends outwardly. In other words, the auger, when considered in cross-section, discloses a slight downwardly slope extending to the outer edge of the auger. This slope permits the heavier particles to travel to the outside under the urging of centrifugal forces and gravity forces. As this movement occurs, the gases are removed from the mud as they rise between the flights of the auger. The gas is drawn from the mud because some separation occurs in the auger. The separation is made complete when the mud spills off the top of the auger and is removed laterally. The auger thus removes bubbles of gas from the mud.
From the foregoing, it will be understood that a conventional auger for transporting drilling mud is not sufficient. It is improbable that a conventional auger arranged within a cylindrical housing and positioned vertically in drilling mud for lifting the mud will effect a good gas separation from drilling mud. Inevitably, there is separation of gas from mud even if the mud is simply stored in an open top container; there is some enhancement in separation if the mud is churned or stirred by any kind of stirring device. However, both these factors are rather minor in importance compared with the total volume of gas that might be entrained in drilling mud. Agitation and exposure of the surface of the drilling mud to atmosphere are not overly enhanced by apparatus of the prior art. This apparatus is a marked advance in that the drilling mud is picked up by a rotating helical screw, the flights of the screw being shaped in such a manner as to initiate separation of the mud and gas, and the screw being further arranged within a vented and ducted housing whereby extracted gas is safely removed. The risk of explosion is reduced in the near vicinity and the gas is removed safely; the mud is nearly restored to or near its original and intended density or weight.
The present apparatus is thus summarized as a degasser which is comprised of an elongate cylindrical tubular housing which encloses a shaft. It is open at the top and bottom. The shaft supports the flights of a helical screw, the preferred form of the apparatus comprising an elongate helical screw wherein the flights are spaced widely at the bottom and they are closer together at the top. Moreover, the helix is affixed at a downwardly inclined angle to the shaft. The cylindrical housing is hollow and has openings at the bottom. The openings at the bottom receive mud from an intake manifold. The cylindrical housing has openings in the side at the top. The openings which are made in the cylindrical housing at the top void mud which is lifted after degassing. They open into a surrounding delivery chamber. The mud is permitted to cascade downwardly into the chamber and is removed. The chamber has an upper area which is perforated to define an exhaust chamber, and a fan located on the shaft at the top end of the apparatus exhausts air and all desolved gas, the fan being located to vent the exhaust chamber at the top of the cylindrical housing. The vented air and gas mixture is removed through an isolated hood which collects gas and directs it out through the fan and through an outlet.